APPENDIX O5 Australian Giant Cuttlefish Olympic Dam Expansion Draft Environmental Impact Statement 2009 Appendix O 69 70 Olympic Dam Expansion Draft Environmental Impact Statement 2009 Appendix O O5 AUSTRALIAN GIANT CUTTLEFISH This appendix provides a detailed natural history and discusses the potential impact of the proposed desalination plant discharges on the Australian Giant Cuttlefish, Sepia apama, to supplement the material provided in Chapter 16, Marine Environment. It also presents the results of surveys of Giant Cuttlefish habitat and population. O5.1 NATURAL HISTORY OF THE AUSTRALIAN GIANT CUTTLEFISH The Giant Cuttlefish, Sepia apama, is the largest cuttlefish species in the world, with males reaching 1 m in length (cuttlebone to 52 cm), and weighing up to 6.2 kg (Gales et al. 1993). Knowledge of the biology of the Australian Giant Cuttlefish is largely limited to winter when they migrate inshore to spawn (Lu 1998a). Cuttlefish are carnivorous, opportunistic and voracious predators (Lee et al. 1998). They feed predominantly on crustaceans and fish. Giant Cuttlefish are demersal animals that live in close association with (and frequently rest on) the seafloor. They use a range of behaviours to avoid predation, including complex camouflage and hiding within algae or the reef substrate. The species as it is currently understood occurs across the temperate waters of southern Australia from southern Queensland to the mid-coast of Western Australian (Lu 1998b). Recent work, however, has shown that the population that spawns at Point Lowly is one of five genetically different populations existing in southern Australia (B Gillanders, University of Adelaide and S Donnellan, South Australian Museum, pers. comm., 11 December 2007). It has minimal interbreeding with the nearest population just north of Wallaroo. These two populations show some of the hallmarks of separate species, such as genetic separation, separate but adjacent distributions, differences in the morphology that may indicate ecological differentiation and different patterns of sexual dimorphism (B Gillanders, University of Adelaide and S Donnellan, South Australian Museum, pers. comm., 11 December 2007). They grow rapidly but are short lived and appear to be semelparous (die after reproducing only once) (Hall et al. 2007). In Upper Spencer Gulf the population appears to comprise two year classes of both males and females, with some individuals growing very rapidly and maturing within one year, whilst others do not return to spawn until their second year when they are much larger (Hall et al. 2007). Throughout most of its range, Giant Cuttlefish breed as pairs or in small groups, on rocky reef habitats where suitable caves and crevices provide egg-laying shelter (Hall & Fowler 2003). Typical breeding behaviour for Giant Cuttlefish throughout their geographic range consists of males competing for and defending optimal egg-laying caves (Rowlings 1994). Loose aggregations of cuttlefish can form but rarely exceed 10 animals at one location at one time. As the majority of Spencer Gulf has a soft sediment seafloor, there are limited areas of emerged rock where female cuttlefish can lay their eggs. Furthermore, the geology of the Point Lowly reef is such that broken slabs of old seafloor sandstone produce a mosaic of flat rocks perfect for laying cuttlefish eggs on the undersides (Gostin et al. 1984). As a consequence, tens-of-thousands to hundreds-of-thousands of cuttlefish, potentially from a large area, aggregate to mate and breed on a narrow strip of rocky reef close to shore, between 2 and 5 metres in depth, from Whyalla to Point Lowly, covering approximately 61 ha (Hall & Fowler 2003) (see Figure 16.9 in Chapter 16, Marine Environment of the Draft EIS). At Black Point near Port Bonython, densities of over 105 cuttlefish per 100 m2 have been recorded at the peak of the season (Hall and Hanlon 2002). Furthermore, a catch of 250 tonnes of cuttlefish was removed from Point Lowly alone in just 3 months during 1997 (Hall and Fowler 2003). The breeding aggregation at Point Lowly is seasonal and cuttlefish are not resident year-round. In mid to late May cuttlefish start arriving at the Point Lowly reefs to spawn, with peak numbers occurring in late May and June (Hall & Fowler 2003). By July, numbers start to decline (as cuttlefish either die or move away from the area), however some mating and spawning activity continues through to September. Although migratory routes to the breeding grounds have not been determined, it is likely to occur through adjacent deeper waters, since cuttlefish primarily associate with the seafloor. In these areas lower light levels, seagrasses and benthic invertebrate communities may provide cover from visual predators such as fish and dolphins. Spawning and post-spawning cuttlefish are a rich food source for many marine predators including pods of the Bottlenose Dolphin Tursiops aduncus, resident during the cuttlefish breeding season at Point Lowly. During the spawning period, the sex ratio is highly skewed towards males, requiring them to compete for females with elaborate visual displays (Hall and Hanlon 2002). Detailed field studies of the mating system of Sepia apama have observed complex behavioural interactions among small (approx. 12 months old) and large (approx. 18 months old) males and females, which are critical for normal fertilisation and egg laying (Hall and Hanlon 2002), and have provided insights into the sexual selection of cephalopods (Hall and Hanlon 2002, Naud et al. 2004 and 2005, Hanlon et al. 2005). Olympic Dam Expansion Draft Environmental Impact Statement 2009 Appendix O 71 Copulation involves the transfer of a packet of sperm to the female, which is stored in a pouch below the mouth (Hall and Hanlon 2002). During egg laying, the female extracts one egg at a time, and apparently fertilises it by passing the egg over the sperm mass. Each egg is wrapped in a gelatinous capsule and carefully attached to rocky substrate on the underside of a ledge or cave (Cronin and Seymour 2000, Hall and Hanlon 2002). Each female potentially lays hundreds of eggs in a single breeding season (Hall and Fowler 2003). The extremely high cuttlefish densities at Point Lowly appear to have led to the adoption of certain reproductive behaviours not recorded elsewhere across their distribution. Large males either defend egg-laying sites or accompany and guard females as they search for egg-laying sites. Small males (potentially 6 months old) also use colour and shape changes to mimic female cuttlefish as a means of avoiding aggression by large males. This enables them to mate with females when larger males are distracted or engaged in combat displays. Developing eggs gradually swell as the embryo forms, taking approximately four months to hatch, with the latest in early November (Hall and Fowler 2003). The hatchlings emerge at around 12 mm in length (Cronin and Seymour 2000), and are the equivalent of miniature adults. They feed on tiny crustaceans and move off the reef during their juvenile life stage prior to their return the following winter. The mass spawning aggregation is believed to be the only cuttlefish mass breeding aggregation of such density in the world and is recognised as one of the more significant and spectacular natural history events in Australian marine waters by national and international marine biologists (R Hanlon, Marine Biological Laboratory, Woods Hole, USA, pers. comm., 6 June 2007). Each year it attracts hundreds of recreational divers, film crews and researchers from Australia and around the world, contributing significantly to the local economy (Hall 2002). Because cuttlefish are short-lived and only reproduce once, there is no accumulation of spawning biomass from one generation to the next and little buffer against years of poor recruitment or over-exploitation. Any actions that limit their reproductive output (harvesting prior to spawning, interference with spawning behaviours), or recruitment capacity (failure of the eggs or young to reach maturity) during one year will be immediately apparent in the following year (Steer and Hall 2005). Historically the cuttlefish aggregations supported a small commercial bait fishery with annual catches rarely exceeding four tonnes, but this rapidly increased to approximately 250 tonnes in 1997 in an attempt to develop a niche fishery (Steer and Hall 2005). This is the equivalent of up to 250,000 cuttlefish being removed from approximately 61 ha of reef. Over-exploitation quickly occurred and the population of cuttlefish near Whyalla declined severely in the ensuing years (T Bramley, Whyalla Diving Services, pers. comm., 6 June 2007). Concerns were raised relating to the sustainability of this unique resource, particularly as fishers were targeting spawning animals. Seasonal closures were introduced in March 1998, initially encompassing the area immediately near Port Bonython, but were expanded in 1999 to include all of the waters enclosed within the area bound by the Point Lowly lighthouse, the Port Bonython Jetty and the OneSteel jetty at Whyalla (Steer and Hall 2005) (see Figure 16.9 in Chapter 16, Marine Environment). The closure was further amended in 2004 to offer year-round protection, banning the collection of all cephalopods within the aggregation area, effective indefinitely. Following the introduction of the closures, the cuttlefish biomass in the Whyalla/Point Lowly region remained relatively stable between 1999 and 2001 at approximately 200 tonnes (Steer and Hall 2005). A survey in 2005, indicated that the biomass of cuttlefish had decreased by approximately 33% since the previous (2001) survey (Steer and Hall 2005), contrary to anecdotal evidence of increased abundance over the same time period (T Bramley, Whyalla Diving Services, pers. comm., 6 June 2007). Steer and Hall (2005) suggested that the apparent decline in abundance and biomass in 2005 was likely to reflect natural variability and that the long-term effects of illegal fishing remain uncertain. Anecdotal observations from the 2006 and 2007 seasons suggest both increased abundance and return of larger animals (M Norman, Curator of Molluscs, Museum Victoria, pers.